Scintillators are materials that emit flashes or pulses of light when they interact with ionizing radiation. Scintillator crystals are widely used in radiation detectors for gamma-rays, X-rays, cosmic rays, and particles characterized by an energy level of greater than about 1 keV. It is possible to make radiation detectors, by coupling the crystal (or scintillator) with an element for detecting the light produced by the crystal when it interacts, or “scintillates,” when exposed to a source of radiation. The photo-detector produces an electrical signal proportional to the intensity of the scintillation (or light pulses received from the scintillator material). The electrical signal is then processed in various ways to provide data on the radiation.
Inorganic compounds in the elpasolite family (A2BB′X6, wherein A and B represent monovalent cations, B′ represents a trivalent cation, such as rare earth or transition metals, and X represents halogen ions) are promising scintillators for gamma and neutron detection. However, inhomogeneity and poor optical quality are often observed in different regions of single crystal elpasolites that are grown from the melt. Commonly, the first-to-freeze region is cloudy, transitioning to a relatively clear middle region, while the last-to-freeze region may be cloudy to opaque.